24,294 research outputs found
Initial stages of cavitation damage and erosion on copper and brass tested in a rotating disk device
In view of the differences in flow and experimental conditions, there has been a continuing debate as to whether or not the ultrasonic method of producing cavitation damage is similar to the damage occurring in cavitating flow systems, namely, venturi and rotating disk devices. In this paper, the progress of cavitation damage during incubation periods on polycrystalline copper and brass tested in a rotating disk device is presented. The results indicate several similarities and differences in the damage mechanism encountered in a rotating disk device (which simulates field rotary devices) and a magnetostriction apparatus. The macroscopic erosion appears similar to that in the vibratory device except for nonuniform erosion and apparent plastic flow during the initial damage phase
Modelling of Multiple Transverse Cracks In Angle - Ply Laminates
Multiple transverse cracking is one of the most common fai'ure modes in composite laminates. In this paper, transverse crack behaviour in 1±0/90°], angle-ply
composite laminates under uniaxial loading has been studied by 3D finite element method. Energy method is used for calculating strain energy release rate and stiffness
reduction as the crack extends in the width direction. A control volume having a single transverse crack has been used for the analysis. Eight noded isonarametric layered
composite elements with three degrees of freedom per node have been used to discretise the control volume. Load is applied in longitudinal direction via uniform applied
displacements through the ±0 outer layers. Strain energy release rate and stiffness reduction are calculated for different crack lengths, crack densities and fibre orientation angle 0 of the outer layers. From the analysis it has been observed that strain energy release rate increases with the increase in fibre orientation angle 0 of the outer layers. However, the variation of strain energy release rate in width direction is negligible.
Stiffness reduction has been noticed with increase in fibre orientation angle 0 and crack density
Rapid Determination of Copper in Copper Ores
Low grade copper ores and copper ores in association with considerable quantities of other elements such as iron, lead, zinc and vanadium require a separational step wherein copper is generally seperated as sulphide either with sodium thiosulfate or with thiocetamide. In these methods the precipitated copper sulfide is ignited to cupric oxide, dissolved in dilute nitric acid and titrated idometrically. In a recent methorl wet oxidation of precipitated copper sulfide is effected with nitric acid ,and perchloric acid and titrated with disodium ethylene diamine tetraacetate (EDTA). The authors' work on the beneficiation of low grade copper ores. and extraction of copper, from these ores has necessitated developing a rapid and accurate method for the determination of copper. A separational step wherein cupric ion could be preci-pitated as cuprous oxide has been introduced to avoid ignition of copper sulfide to cupric oxide, which is time consuming
Magnetic and electron transport properties of the rare-earth cobaltates, La0.7-xLnxCa0.3CoO3 (Ln = Pr, Nd, Gd and Dy) : A case of phase separation
Magnetic and electrical properties of four series of rare earth cobaltates of
the formula La0.7-xLnxCa0.3CoO3 with Ln = Pr, Nd, Gd and Dy have been
investigated. Compositions close to x = 0.0 contain large ferromagnetic
clusters or domains, and show Brillouin-like behaviour of the field-cooled DC
magnetization data with fairly high ferromagnetic Tc values, besides low
electrical resistivities with near-zero temperature coefficients. The
zero-field-cooled data generally show a non-monotonic behaviour with a peak at
a temperatures slightly lower than Tc. The near x = 0.0 compositions show a
prominent peak corresponding to the Tc in the AC-susceptibility data. The
ferromagnetic Tc varies linearly with x or the average radius of the A-site
cations, (rA). With increase in x or decrease in (rA), the magnetization value
at any given temperature decreases markedly and the AC-susceptibility
measurements show a prominent transition arising from small magnetic clusters
with some characteristics of a spin-glass. Electrical resistivity increases
with increase in x, showed a significant increase around a critical value of x
or (rA), at which composition the small clusters also begin to dominate. These
properties can be understood in terms of a phase separation scenario wherein
large magnetic clusters give way to smaller ones with increase in x, with both
types of clusters being present in certain compositions. The changes in
magnetic and electrical properties occur parallely since the large
ferromagnetic clusters are hole-rich and the small clusters are hole-poor.
Variable-range hopping seems to occur at low temperatures in these cobaltates.Comment: 23 pages including figure
Disentangling the dominant drivers of gravity wave variability in the Martian thermosphere
In this study, we extracted the amplitudes of the gravity waves (GWs)from the
neutral densities measured in situ by the neutral gas and ion mass spectrometer
aboard the Mars atmosphere and volatile evolution mission. The spatial and
temporal variabilities of the GWs show that solar activity (the F10.7 cm solar
flux corrected for a heliocentric distance of 1.66 AU), solar insolation, and
the lower atmospheric dust are the dominant drivers of the GW variability in
the thermosphere. We developed a methodology in which a linear regression
analysis has been used to disentangle the complex variabilities of the GWs. The
three dominant drivers could account for most of the variability in the GW
amplitudes. Variability caused by the sources of GWs and the effects of winds
and the global circulation in the mesosphere and lower thermosphere are the
other factors that could not be addressed. The results of the present study
show that for every 100 sfu increase in the solar activity, the GW amplitudes
in the thermosphere decrease by ~9%. Solar insolation drives the diurnal,
seasonal and latitudinal variations of ~9%, ~4% and ~6%, respectively. Using
the historical data of the dust opacity and solar activity, we estimated the GW
amplitudes of the Martian thermosphere from MY 24 to MY 35. The GW amplitudes
were significantly reduced during the maximum of solar cycle 23 and were
highest in the solar minimum. The global dust storms of MY 25, 28, and 34 lead
to significant enhancements in the GW amplitudes.Comment: Accepted for publication in the astrophysical journal; 18 page
Training needs assessment in Malaysia: Exercise held at Kuala Lampur and Kota Bharu from 13th October 1989
Training / Irrigation / Evaluation / Malaysia
Multi component one pot synthesis and characterization of derivatives of 2-amino-7,7- dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile and study of anti-microbial activity
An efficient and convenient procedure has been described for one-pot multi-component synthesisof tetrahydrobenzo[b]pyrans known as 2-amino-7,7-dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile which can be obtained from the reaction of substituted aromatic aldehydes, dimedone, malonitrile, in the presence of base such as potassium tertiary butoxide and THF in methanol as solvent at RT condition. All the compounds were examined by advanced spectroscopic data (1H NMR, 13C NMR and LCMS) and the structural determination was evaluated by elemental analysis. In addition to this, all the newly synthesized compounds were examined for their antibacterial activities and antifungal activity by disc diffusion method against the organism of Aspergillus niger and Candida ablicans L. KEY WORDS: Aromatic aldehydes, Dimedone, Malonitrile, Potasium tertiary butoxide, 2-Amino-7,7-dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile, Anti-microbial activity Bull. Chem. Soc. Ethiop. 2018, 32(1), 133-138DOI: https://dx.doi.org/10.4314/bcse.v32i1.1
Amino acid imbalance and tryptophanniacin metabolism: I. Effect of excess leucine on the urinary excretion of tryptophan-niacin metabolites in rats
The effect of feeding excess leucine on the urinary excretion of tryptophan-niacin metabolites and nitrogen was studied in young and adult rats. Urinary excretion of quinolinic acid and N'methylnicotinamide was increased in both young and adult rats when L-leucine was added at 1.5% level to a 9% casein diet. Quinolinic acid excretion was more markedly affected in young rats, whereas N'-methylnicotinamide excretion was more affected in adult rats. Isoleucine counteracted the effect of leucine in young rats. Nitrogen excretion increased on leucine feeding in adult rats but not in young rats. Adult rats fed a jowar (Sorghum vulgare) diet tended to excrete relatively more N'-methylnicotinamide and niacin than when fed a wheat diet
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